A measurement of the proton structure function F2(x, Q2) at low x and low Q2 at HERA

The results of a measurement of the proton structure function F2(x,Q2) and the virtual photon-proton cross section are reported for momentum transfers squared Q2 between 0.35 GeV2 and 3.5 GeV2 and for Bjorken-x values down to 6 × 10−6 using data collected by the HERA experiment H1 in 1995. The data represent an increase in kinematic reach to lower x and Q2 values of about a factor of 5 compared to previous H1 measurements. Including measurements from fixed target experiments the rise of F2 with decreasing x is found to be less steep for the lowest Q2 values measured. Phenomenological models at low Q2 are compared with the data.